This invention relates to radio receivers having dual bandwith intermediate frequency (IF) stages and, more particularly, to a bandwidth switching system to provide improved IF bandpass selectivity.
It is well known that there are radio broadcast receivers which offer switchable IF selectivity. In such prior art receivers, typically an interference-free radio signal condition is obtained with a narrow band-pass IF filter and higher fidelity is obtained with a wide bandpass IF filter. However, the existing systems have not been altogether satisfactory in providing better audio quality, especially when listening to a relatively weak station or channel which is located adjacent to a relatively strong station or channel. Furthermore, in many prior art IF selectivity arrangements, the choice of IF selectivity is usually dependent upon the signal characteristics of the selected channel and not upon adjacent channel characteristics or interference.